French police have fired tear gas to disperse dozens of protesting steelworkers seeking talks with President Nicolas Sarkozy.

The protesters were marching toward Sarkozy's campaign headquarters in Paris on Thursday when riot police started dispersing them.

Some of the workers tried to break through a police line to reach the campaign headquarters in a middle-class neighbourhood of southwest Paris, but the president was on the campaign trail outside the capital.

With five weeks to the presidential election, Sarkozy said that the 150 workers who had come to Paris were more interested in playing politics than in finding solutions for the ArcelorMittal steel mill Florange in eastern France.

But CFDT union official Edouard Martin blamed Sarkozy for the workers' treatment, saying it made a mockery of his claim to defend the interests of working-class French.

"For four weeks we've been on strike and we haven't harmed anyone and now he gasses us, 'The candidate of the people'," said Martin.

The Florange steel mill, whose blast furnaces were idled until further notice late last year due to a lack of orders, has come to symbolise France's industrial decline ahead of the two-round April 22 and May 6 elections.

Sarkozy trailing

Sarkozy's Socialist rival Francois Hollande has seized on the mill's plight as a sign of the president's failure to halt the decline of France's industrial base, which has shed over 350,000 jobs since Sarkozy took office in 2007.

The president is trailing Hollande in opinion polls although the margin is narrowing. A survey released on Wednesday showed Hollande and Sarkozy tied for the first round on 28 per cent each, with the Socialist winning a second round by 54 per cent to 46.

Sarkozy said he would be happy to meet on Monday with workers truly interested in the mill's fate and not stirring up trouble.

"I know that the Florange workers who are worried about their jobs don't like their suffering to be used," he told journalists. "The unions should defend workers interests not play politics."

Sarkozy said at the start of the month that he had secured a commitment from ArcelorMittal to invest $22m in the plant and restart it in the second half of the year.

However, the company later said that would depend on the economic conditions being there.

Three killed

Separately, at least three French soldiers have been killed and another seriously wounded in a drive-by shooting near a military base in the southwestern city of Montauban, a state official said.

Details were not immediately clear, but the local official told the AFP news agency that Thursday's shooting took place on a street not far from the base housing the 17th Parachute Engineer Regiment.

The official said a scooter-rider, wearing a helmet with visor, opened fire on the three uniformed soldiers on a street near businesses and a bank branch, then fled.

Authorities launched an extensive search for the gunman involving a large number of police and national gendarmes, the official said.

The incident follows another shooting on Sunday that saw a 30-year-old soldier shot dead by an assailant on a motorcycle in a residential area of Toulouse, 46km south of Montauban.

Prosecutors said they were considering a number of possibilities in that shooting, including that it was the result of a personal dispute.